Lead engineer for Microsoft Identity Services Sarat Subramaniam, goes over Azure Active Directory B2B collaboration, which as of 4/12/ 17 is now generally available.
If you are unfamiliar with Azure AD B2B:
It is service that simplifies the secure sharing of your Apps and services with your external business partners and colleagues. It allows users to easily share common Apps and services to collaborate with their peers and IT to add and manage these external users without having to add them to the corporate directory or requiring partners to have Azure Active Directory in place. Further, conditional access authorization policies - including Multi-factor authentication enabled by Azure Active Directory keep data safe.
More information can be found here: aka.ms/AddB2Busers